The present invention relates to a wide area cordless telephone system.
A cordless telephone system is known which comprises a stationary access unit to which a telephone line from a switching system is connected and a transportable cordless unit which establishes a two-way radio channel to the access unit as long as it stays within a specified range.
A wide area cordless telephone system has recently been proposed to provide wide area services for corporate premises as part of PBX (private branch exchange) telephones. According to the proposed scheme, the whole area of the system is divided into a plurality of local areas. A plurality of fixed access units are located in each local area. Each access unit of a given local area establishes a radio channel to any of the home position cordless telephones that belong to the given local area as well as to non-home position roaming cordless telephones that enters that local area. The home position cordless telephones have corresponding line terminals in the associated PBX or in the public switched telephone network. Each cordless telephone has a multi-channel access capability to have access to any of the access units and includes a manually operated key that is operated by the user when a request is made for registration of the location of his telephone. Since the cordless telephones can access any of the access units, a pre-dialing switching stage is provided in each local area to establish a connection between each access unit and a line terminal of PBX or public switched network so that the telephones can be connected to their corresponding line terminals of the PBX or switched network before dialing procedure begins. A controller is provided to register the cordless telephones where they are located in their own local area. In order to allow cordless telephones to roam from one area to another, line terminals of the PBX or public switched network are reserved and the controller assigns a reserved line terminal to an entering non-home position telephone and communicates this fact to other local areas.
However, if a cordless telephone crossing a boundary between adjacent local areas sends a registration request to elicit a response, there is a likelihood of the request being received simultaneously by two or more access units of the adjacent areas and plural responses are returned which indicate the grant of registration in respective local areas, thus resulting in "double" registrations.